1. Field of the Invention
This invention relates to method and apparatus for the spinning of fibres from molten polymeric fluids. More particularly, it relates to method and apparatus for the electrostatic spinning of fibres from molten rapidly crystallizing fibre-forming thermoplastic polymers.
2. Description of the Prior Art
Fibre spinning is the basis of a major world-wide industry. As is well known to those skilled in the art, in the conventional fibre spinning process, the polymer is melted and the molten polymer is then forced through a spinneret by some pumping mechanism, usually involving high pressures. This is followed by the cooling, drawing and winding up of the continuous filament on a spool. These spinning processes are broadly applicable to polyolefins, polyamides, polyesters and indeed to the whole range of rapidly crystallizing fibre-forming thermoplastic polymers.
As is also known to those skilled in the art, the usual method for producing an oriented polymer filament is to extrude molten polymer through an orifice and then to wind up the crystallized filament so produced at a rate faster than the extrusion velocity. An improvement in such process is taught in the Frank et al British Pat. No. 1,431,894, which provides method and apparatus in which the molten crystallizable polymer is forced through a constricted orifice at a sufficiently high pressure so as to produce a sufficiently high velocity gradient in the polymer in the region of the orifice along a line of uniaxial extension or pure shear that the temperature can be selected so as to provide continuous production of a core of crystalline polymer within the melt emerging from the orifice.
However, it is believed that such conventional spinning processes may be unsuitable for fibre spinning with very high molecular weight materials of all kinds, or with materials having very strong polar force bonding. It is believed that, for processes to involve the generation of a sufficiently high shear field to produce sufficient elongation flow in the polymer melt, the process would require a very high extrusion pressure. This can result in flow instability problems.
It is now known [see G. I. Taylor, "Electrically Driven Jets" Proc. Roy. Soc. London A 313,453-475 (1969)] that fine jets of monomeric liquids can be drawn from conducting tubes by electrostatic forces. As the potential of the conducting tube rises, the fluid becomes nearly conical and fine jets come from the vertices.